The invention relates to the regeneration of ion exchange materials.
In water treatment plant, for example boiler water treatment plant including mixed-bed condensate polishers, deionised water is used for the transfer, washing and rinsing operations during regeneration of the condensate polisher ion exchange materials. The regeneration of the materials is usually performed externally of the polisher service vessel. The deionised water for the regeneration operations is taken, for example, from the boiler feed water make-up supply, the final stage of which supply is commonly a mixed-bed deionisation unit.
In each regeneration cycle, for example, exhausted ion exchange materials are classified into layers by backwashing. Next, the materials are separated by a transfer flow of water to pass one type at least to a separate vessel. A very effective way, for example, of controlling the transfer stage is described in U.S. Pat. No. 4,298,696 J. R. Emmett, patented Nov. 3, 1981 in which the conductivity of the transfer water flow is monitored to determine when the last of one type, say cation material for example, has left the classifier.
The conductivity of the transfer water is very low indeed so that only extremely slight changes in conditions can cause the conductivity to change by several hundred percent.
In the instance of transfer water derived from a boiler feed water make-up supply, as the ion exchange materials in the mixed-bed make-up unit become exhausted, the ion concentration of the feed water changes. Additionally, in such a system, water from the make-up supply is stored in a storage tank. The water in the tank absorbs carbon dioxide and other gases to a degree dependent on time and temperature, for example, and when the water for the regeneration of the condensate polisher is changed from the normal flow from the mixed-bed make-up unit to flow from the storage tank, the ion concentration of the water for the condensate polisher regeneration changes.
Such changes although small in absolute terms may cause a parameter such as conductivity, for example, which is dependent on ion concentration, to change by as much as 600%. The changes are variable, so that in successive regeneration cycles the conductivity, for example, of the transfer water is unknown and may lie anywhere between a lower value and a higher value which have a ratio of as much as 1:6. Such spurious and uncontrolled changes in ion concentration are due generally to what may be termed "source changes" affecting the ion concentration of the water before the water is used to transfer ion exchange material.
Such wide percentage variation in the conductivity of the transfer water itself would mask the change in effective conductivity of the transfer flow which is required to be detected in order to indicate thaat the material being transferred in the water has changed from one type to the other.
The object of the invention is to eliminate or render negligible the effect of spurious uncontrolled source changes on the ion concentration of the transfer water.